Sorting items of mail in a distribution order is understood to mean the procedure of bringing the items of mail to be distributed into an order which corresponds to the order of the distribution stopping points, for example in accordance with house numbers/mailboxes. These distribution stopping points are walked to or driven to by the distributor systematically in his delivery area. The distribution stopping point is in this case not an absolute sorting destination but a relative position in the distribution order.
Manually, this sorting is very complicated. By means of a sorting machine, this sorting can be carried out with considerably less expenditure on time, the sorting being based on a sorting plan. The sorting plan is a list which performs the allocation of addresses to the defined delivery stopping points, that is to say describes the order. In the machine, it is the relation between the machine-readable address code and the sequence number. Since the number of distribution stopping points is normally larger than the number of sorting compartments of the sorting machines, the distribution order sorting of the items of mail to be sorted is carried out in a plurality of sorting passes. In the process, the items of mail are in each case fed to the sorting machine again in the order sorted in the preceding pass.
The following example illustrates how sorting is carried out in two passes. Assuming that a specific number of items of mail are to be distributed to 20 distribution points. In this case, it is sufficient to have 4 sorting compartments in the first sorting pass and 5 sorting compartments in the second sorting run, since 4×5=20.
OriginalModifiedSortingSortingDeliverydistributiondistributioncompartmentcompartmentcodeorderorder sortingsorting(ZIP code)numbernumberpass 1pass 278453:332/025 11A1 (A)178453:332/027 21B2 (B)178453:332/029 31C3 (C)178453:335/102 41D4 (D)178453:335/104 52A1 (A)2............78453:347/045195C3 (C)578453:347/047205D4 (D)5
In the first sorting pass, the items of mail are distributed in accordance with the capital letters into four sorting compartments, that is to say the first sorting compartment received all the items of mail which contain an “A”, the second sorting compartment receives all items of mail which contain a “B” and so on. The sorting compartments are emptied and the items of mail are put into the physical input again, specifically beginning with the items of mail from the first sorting compartment (“A”), then with those from the second sorting compartment (“B”) and so on. During the second sorting pass, the items of mail are distributed in accordance with the number into 5 sorting compartments, that is to say the first sorting compartment receives all the items of mail which contain a “1” and so on. Since, after the first sorting pass, the items of mail which contain an “A” are already located in front of the items of mail which contain a “B”, sorting compartment 1 then firstly receives the items of mail which contain “1A”, then “1B” and so on. The same applies in an analogous way to all the other compartments, so that the distribution order sorting is completed after the second sorting pass. According to the prior art, it is necessary to draw up an allocation table, what is known as the sorting plan, which determines an unambiguous relationship between the delivery code, that is to say the ZIP code, and the sorting compartments within one pass. A variant of this method merely produces a relationship between the delivery code and the distribution order number. The sorting compartment allocation is performed during the sorting. Assuming that the distribution order number of a recognized delivery code is known, it is provided by the sorting plan and then has to be translated into a compartment number. The distribution order number in itself can be viewed as a combination of compartment allocation rules which here, for example, exhibits the following features. The machine has 10 compartments (consequently, the distribution order number is a decimal number), the compartments are designated 0 . . . 9, the number of passes is equal to the number of decimal places in the distribution order partial order number. Example: the distribution order number 528 is sorted in three passes, into compartment 8 in the first sorting pass, into compartment 2 in the second sorting pass, into compartment 5 in the third sorting pass. In another machine with 64 available compartments in the first sorting pass and 30 in the second sorting pass, this same distribution order number (528) will be distributed as follows: into compartment 16 in the first sorting pass, into compartment 8 in the second sorting pass. In general, it is true that the number of digits corresponds to the number of passes needed, the numeric base of each digit corresponds to the number of compartments available in the respective sorting pass.
This consideration initially disregards the number of items of mail which are to be sorted per distribution order number. Under the assumption that there is a largely equal distribution of the quantities of items of mail, for example on average 3 items of mail for distribution order number, by considering the total quantity of items of mail, the number of sorting compartments and their size, a sorting machine can be utilized in an optimum way without a compartment-full situation occurring. Sorting compartment overflows which occur sporadically can be intercepted by the use of overflow compartments.
During this sorting according to the prior art, sorting compartments can overflow or can also be filled with only a very small number of items of mail. Because of the possible overflow, overflow compartments are provided. However, this reservation of overflow compartments means a reduction in the sorting capacity of the sorting machine with regard to the possible distribution stopping points.
Successive optimization of the sorting plan can reduce the number of necessary overflow compartments, but not replace them, since the composition and the extent of the items of mail remain unknown. When the sorting machine is emptied and the contents of sorting and overflow compartments are brought together, operating errors can occur which, under certain circumstances, change the order to such a great extent that repetition of the sorting becomes necessary.
The use of overflow compartments secondly does not guarantee that no further compartment-full situations can occur. In a method for avoiding compartment overflows according to U.S. Pat. No. 5,363,971, the ZIP codes are read and assigned to distribution stopping points. Then, by means of a microprocessor, the assignment of the ZIP codes to the distribution stopping points is modified in order to optimize the distribution of the items of mail in the compartments. This is done by not all the possible distribution stopping points being used but reserve stopping points being provided. By means of a specific allocation of the ZIP codes to the distribution stopping points and by placing the reserve stopping points between the associated distribution stopping points, it is possible to distribute the items of mail in an improved manner, in order to minimize the probability of compartment overflow. As a result, in the original compartment combination, only the remaining residual quantity is still sorted, which results in undesired nonuniform compartment filling. Given only low levels in the sorting compartments, time losses arise, since the time expended for emptying a little-filled compartment does not differ or differs only insignificantly from emptying a full compartment.
In DE 196 25 007 A1 a method for distribution order sorting is described in which, in order to avoid compartment-full situations, by means of iterative search steps in a simulation of the sorting operation before the sorting operation carried out by the sorting machine, the items of mail of each original distribution starting point are distributed to modified distribution starting points in such a way that the sorting compartments can accommodate the items of mail without any overflow. This iterative simulation is very time-consuming, so that, in a specific time interval, only a limited difference in quantity between the distribution stopping points can be compensated for.
In DE 196 47 973 C1, a description is given of using quantity statistics of the daily occurrence of items of mail from the past in the generation of sorting plans and, in DE 43 02 231 A1, there is an exposition of basing the sorting plan on statistical averages for the occurrence of postal items for specific destinations. However, how the sorting plans are configured in an optimum way with this information is not specified.